Response of two Afromontane coniferous tree species to light and nutrient supply.

We studied the responses to light and nutrient availability of the two Afromontane conifers Juniperus procera Hochst. ex Endl., reputedly a shade-intolerant species, and Afrocarpus gracilior Polger C.N. Page, a shade-tolerant species. The species behaved similarly in response to light and nutrient availability. Both species showed positive growth rates at photon fluxes of 0.6-0.8 mol m(-2) day(-1). Maximum relative growth rates of 0.15 week(-1) were attained at an irradiance of 8 mol m(-2) day(-1) in the high-nutrient supply treatment. The growth response to high-nutrient supply was achieved by an increase in leaf area ratio rather than by an increase in net assimilation rate. In a 10-week growth experiment, both species displayed an increase in stem extension rate in response to a low red/far-red ratio (0.09) at low irradiance, and A. gracilior also responded by increasing its specific leaf area. Similiar findings were observed in a short-term experiment in which internodes were laterally irradiated.